The present invention relates to blow molding, and more particularly to an apparatus and method for strengthening a portion of a blow molded article.
Blow molding is a common process for forming articles such as plastic bottles. This process typically begins with forming a preform by injection molding. Preforms are usually shaped like a test tube, with the open end having a neck similar to the neck of a molded plastic bottle. After the preforms are formed, they are placed in a blow molding machine, usually by attaching the neck of each preform to a carrier for transport through the machine. The preforms are then transported through a heating station, where they are heated by a number of heaters, and then transported into a blow molding station. In the molding station, the preforms are inserted into a mold cavity and then blown and stretched into the shape of the mold cavity. The molded articles are then cooled, removed from the machine and distributed for use.
To ensure that heat from the heaters is distributed evenly to each of the preforms, blow molding machines often rotate the preforms as they pass through the heating station. Rotation may be provided by a number of conventional methods, such as a belt that is driven by pulleys and contacts each preform carrier.
One common problem that arises with blow molded articles, especially plastic bottles, is that they often dent or crumple during packaging, shipping, or use. Often this damage is due to improper handling of the bottle. In many cases, the damage could be prevented if the bottles were stronger. To address this problem, some manufacturers have attempted to add strength to blow molded bottles during the blow molding process. One attempted solution is to mold ribs or other features into the walls of the bottle to add rigidity to those areas of the bottle. This method is effective at strengthening the bottle, but the ribs are often unsightly and therefore unsuitable for many applications. Another attempted solution is to increase the thickness of the entire bottle. This too is effective at strengthening the bottle, but it requires much more material per bottle. When factored over the thousands of bottles that are often made for a given application, the increased material costs from these methods can drive the price of these bottles out of the targeted market.